Enrolling in Medicare Part D isn’t a “one-and-done” decision. Leaving your plan on autopilot during open enrollment (Oct. 15-Dec. 7) could cost you hundreds in unexpected premiums and out-of-pocket fees. A different plan might offer a much better deal — especially if you’ve started new medications or your current drugs have transitioned to generic over the past year.

Between major legislative redesigns — like the permanent end of the infamous “donut hole“ — and routine plan changes, the Medicare Part D coverage landscape shifts every year. Even if your health hasn’t changed, your insurer’s formulary tiers, preferred pharmacy networks and deductibles likely have.

To make sure you aren’t overpaying, use the official Medicare Plan Finder tool to compare coverage in your area. By entering your specific medications, dosages and preferred pharmacies, you can see your true costs for 2027.

Here are the remaining five of 10 critical Medicare Part D rules and changes you need to know before enrolling.

6. There are no spousal discounts

Most spouses don’t take the same medications. One plan may have much better coverage for your drugs while another may be better for your spouse’s needs.

You should each look up your drugs and dosages using the Medicare Plan Finder to estimate out-of-pocket costs for the plans in your area.

Before you and your spouse sign up for plans with different preferred pharmacies, consider if you are willing to go to more than one pharmacy to fill your monthly prescriptions. Some plans only give you the best rates if you use their network.

7. You can opt into the Medicare prescription payment plan

This optional, fee-free program allows you to spread your drug costs out into capped monthly installments over the year instead of paying a massive chunk all at once at the pharmacy counter. You can directly opt in to the Medicare prescription payment plan through your Part D plan sponsor.

If you opt into the Medicare Prescription Payment Plan, you won’t pay at the pharmacy counter; your plan will be notified automatically. Instead, your insurer will send you a monthly bill detailing what you owe for your prescriptions with instructions on how to pay.

If you used this program last year and stayed with the same plan, your enrollment automatically renews; however, if you switch Part D plans during open enrollment, you must manually opt in again with your new insurer.

8. The options for stand-alone plans are shrinking

Over the last five years, the number of stand-alone plans available to the average Medicare beneficiary decreased from 30 in 2021 to 11 in 2026, according to KFF, a health information organization formerly known as the Kaiser Family Foundation.

From 2025 to 2026, plan availability decreased by 22%. With fewer plans to choose from, you cannot assume your current plan will remain competitive or even exist.

9. Premium subsidies will end this year

An IRA premium stabilization demonstration, established in 2024 to prevent substantial premium increases due to the Part D benefit redesign, subsidized and stabilized average monthly premiums in 2025 and 2026. The demonstration has ended, and no subsidies will be paid to offset premium increases in 2027. CMS scaled back that support earlier this year, stating in a memo that reducing federal subsidies is intended to help the Part D program “return to operating under regular market conditions.”

The federal government provides roughly $190 in annual premium subsidies per enrollee under the stabilization demonstration in 2026, based on a projected $16 per member per month premium reduction, according to KFF.

“Without these subsidies in place for 2027, some Part D stand-alone drug plan enrollees could see a larger premium increase for drug coverage next year than they’ve faced in recent years, though plan-specific premiums are not yet known,” says Juliette Cubanski, vice president and director of the Program for Medicare Policy at KFF.

10. Avoid the permanent late enrollment penalty

If you don’t enroll in Part D when you are first eligible, and you go 63 consecutive days or more without“creditable” drug coverage (coverage deemed as good as or better than Medicare’s standard), you will face a permanent late enrollment penalty when you eventually sign up. The penalty is assessed per month for each month you went without coverage and is added directly to your monthly premium for as long as you hold a Part D plan.

(Donna LeValley is a retirement writer for Kiplinger.com.)

©2026 The Kiplinger Washington Editors, Inc. All rights reserved. Distributed by Tribune Content Agency, LLC.